Most of us have taken antibiotics or given them to our children in hopes of getting well without any thought about where those antibiotic compounds in our medications might eventually end up. But, Atlas-award winning researchers writing in Microchemical Journalsay that a good portion of those drugs will make their way to wastewater treatment plants and then out into the environment, where they can do harm to microbes that are essential to a healthy environment.

“The amount of antibiotics is very, very low—there are normally nanograms per liter of these molecules found in natural environments,” said Paola Grenni, a microbial ecologist at the National Research Council’s Water Research Institute in Italy. “But the antibiotics and also other pharmaceuticals can have an effect even in low concentrations, the so-called environmental side-effects.”

When people take antibiotics, their bodies break down and metabolize only a portion of the drugs. The rest is excreted and enters wastewater. The trouble is that wastewater treatment plants aren’t designed to fully remove antibiotic or other pharmaceutical compounds. Some of those compounds are also persistent, meaning that they aren’t readily degraded in the environment. As a result, those compounds can accumulate in natural systems.

There’s a special reason to suspect that antibiotics could be doing harm to microbes upon reaching natural aquatic or soil environments. That’s because, unlike other pharmaceuticals, antibiotics are specifically designed to kill bacteria in one way or another, by altering or damaging bacterial cell membranes or blocking the microbes’ ability to build nucleic acids, proteins, or essential metabolites.

That’s a big concern, Grenni says, because the vast majority of microbes aren’t in the habit of making people sick. Many microbial species found in the environment are beneficial, playing important roles in natural cycles of nutrients, primary production and climate regulation. Some microbes also degrade organic contaminants, such as pesticides.

The review paper published by Grenni along with colleagues Valeria Ancona and Anna Barra Caracciolo, includes long lists of antibiotic compounds and their active ingredients. Some of those medications are used to treat people. Many others are used in veterinary medicine, and especially to treat farm animals including cattle, pigs, and poultry. In some countries, including the United States, antibiotics are used routinely in large quantities to make farm animals grow bigger faster, not only to treat illness.

The researchers note that certain antibiotics, including macrolides, quinolones, sulfonamides, and trimethoprim, are most frequently found in nature. That’s because of their common use in both human and veterinary medicine and because they persist for long periods of time in aquatic environments. As a result of their steady introduction into the environment, microbes in soil and water are chronically exposed to those substances.

Those antibiotics can have various effects on microbes that come into contact with them. In some cases, low levels of antibiotics might kill certain microbes, or alter the natural composition of communities in damaging ways. Some microbes might evolve means to degrade those antibiotics. At the same time, antibiotic exposure can select for microbes carrying genes that allow them to resist antibiotics.

In fact, the researchers write, antibiotic resistance genes can be thought of as a new kind of environmental “pollutant.” Once in the environment, those resistance genes tend to stick around. They can even spread from one bacterial species to another, presenting new kinds of risks to the environment and to human and animal health.

The release of antibiotics into natural systems is a recent problem by evolutionary standards. The consequences of this real-life experiment aren’t fully known. Grenni and colleagues say there’s a need for more specific protections of environmental microbes given their importance to functioning ecosystems. She calls for Ecological Risk Assessments to establish the effects of antibiotics, both those that are new and those that are untested despite the fact they have long been in use.

It’s important for nations to work to reduce unnecessary antibiotic use and the release of those antibiotics that are needed into the environment. Efforts should be made to equip wastewater treatment plants for removal of those compounds and to devise methods to improve the degradation of antibiotics once they reach natural environments.

Members of the public can help by taking care to use antibiotics only when they are truly needed, and by disposing of expired medications properly. Take them to the pharmacy, Grenni says. And, whatever you do, “don’t put them down the toilet.”

Grenni says more research and researchers will also be key. “There are only a few researchers working in this field, but it’s very important,” she said. “We need to know the different molecules we normally use that are in the environment and the effect they have. We need more research in this field.”

A Conversation with Paola Grenni

Paola Grenni at the National Research Council’s Water Research Institute spoke with us about antibiotics and the ecological effects they’re having on natural ecosystems. Listen now.

Atlas: Where do the antibiotics we take end up?

Paola Grenni: Many people use antibiotics for different issues but when you use this kind of pharmaceutical they can reach the environment. When you take an antibiotic, your body metabolizes only a part of these molecules. Another part of the amount that you take can reach the wastewater and the treatment plant. Wastewater treatment plants in most cases are not able to degrade these molecules, so they can consequently reach the surface water and other ecosystems.

Atlas: You talk about the possible influence of these compounds on natural bacterial communities. For people who may not be accustomed to thinking about the value of natural bacterial communities, what kinds of concerns does that raise?

Paola Grenni: First of all, bacteria that are in natural environment are of different kinds of course. Not all bacteria cause disease. Indeed, only a few groups of them are harmful for human and animal health. There are many bacteria in the environment that are involved in maintaining multiple ecosystem functions and services simultaneously, including natural cycles of nutrients (e.g. carbon, nitrogen, and phosphorus), primary production, litter decomposition, climate regulation and degradation of different organic contaminants. These bacteria are very important for the health of the environment. If antibiotics can reach the environment, they can kill this kind of bacteria, altering some natural cycles of nutrients, for example, or hampering the degradation of other organic contaminants of human origin. In other cases, these antibiotic molecules can select bacterial strains able to degrade these molecules and select for bacteria carrying antibiotic resistance genes, which in turn decrease the efficacy of antibiotics against some disease.

Atlas: You note that for the first time in legislative history one class of macrolide antibiotics are included on a watch list of substances that may pose a risk to aquatic environments. Tell me about that. What triggered the attention to this group of antibiotics?

Paola Grenni: This group of antibiotics has been a focus for the European Union because there are many studies in which they found very high quantities of these antibiotics in the environment. That’s because the degradation of these molecules is very, very low and so the problem is they are persistent molecules. Moreover, these substances are suspected of posing a significant risk to aquatic organisms and mammals and there is not enough information to assess their EU-wide exposure.

Atlas: What can be done? Is there a way to keep antibiotics out of natural systems or to at least reduce them?

Paola Grenni: First of all, do not overuse antibiotics. Use antibiotics only if your doctor says you have to use them. In many countries, especially in America, antibiotics are used not only against some disease but also to encourage the growth of the animals such as pigs or chickens. The use of antibiotics in this case is not very good of course. So we have to reduce the use of antibiotics in cases where they are not important for your health or the health of the animals. The second point is we need to have wastewater treatment plants that are able to degrade these kinds of molecules. This is a crucial point in order to diminish the amount in the environment.

The Microchemical Journal is a peer-reviewed journal devoted to all aspects and phases of analytical chemistry and chemical analysis. The Microchemical Journal publishes articles, which are at the forefront of modern analytical chemistry and cover innovations in the techniques to the finest possible limits. This includes fundamental aspects, instrumentation, new developments, innovative and novel methods and applications including environmental and clinical field.

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Kendall Morgan, PhD, is a scientist turned science writer via the Science Communication Program at the University of California, Santa Cruz. Her work has been featured in publications including Big Science Media's Genome, Cancer Today, The Scientist, Science News, Science Now, and by organizations including Addgene and the Life Sciences Foundation. She lives in Durham, NC.